Rob, yes you can in excel, raise all the columns of the traces by the quantity you want then reopen in graced.

Roo, if you change the traces position and create any camber, then the value of the cambers will be different.
If you add a trace between 2 already there, the value of the height will be exactly in the middle so, if you then move the trace to adjust its position, you will need to fix all its elevations; to avoid this you can keep on add and erase a trace in GPLtrk without move them until is in the position that you like so it will be "perfectly flat" between its 2 adjacent traces unless you move it .
If you add a section in the GTk. it will be flat and the previous one will end where you did choose before so you will need to fix the elevations of those 2 sections.

Yes, that is correct, although if you have a loose trk file in the track folder then I think that GPLRA reads this one first in preference. Certainly Grand Prix Legends will always use a trk file that is outside the DAT file in preference to one inside the DAT and it only looks in the DAT file if there is not a loose file in the folder.

Once scaled you then need to "treat" all the curved sections by add some units then go back to the original value (I use to add 1 to the second number since I find it easy to do: 234321 becomes 244321, then go back to 234321).
This is needed to revert the length to its real value; if yo don't do this, data of the GTK will not correspond to data in the final TRK.
You can do this when you zero all the gaps.